7,550 research outputs found
Temporal Aperture Modulation
The two types of modulation techniques useful to X-ray imaging are reviewed. The use of optimum coded temporal aperature modulation is shown, in certain cases, to offer an advantage over a spatial aperture modulator. Example applications of a diffuse anisotropic X-ray background experiment and a wide field of view hard X-ray imager are discussed
Pre-enriched, not primordial ellipticals
We follow the chemical evolution of a galaxy through star formation and its
feedback into the inter-stellar medium, starting from primordial gas and
allowing for gas to inflow into the region being modelled. We attempt to
reproduce observed spectral line-strengths for early-type galaxies to constrain
their star formation histories. The efficiencies and times of star formation
are varied as well as the amount and duration of inflow. We evaluate the
chemical enrichment and the mass of stars made with time. Single stellar
population (SSP) data are then used to predict line-strengths for composite
stellar populations. The results are compared with observed line-strengths in
ten ellipticals, including some features which help to break the problem of
age-metallicity degeneracy in old stellar populations. We find that the
elliptical galaxies modelled require high metallicity SSPs (>3 x solar) at
later times. In addition the strong lines observed cannot be produced by an
initial starburst in primordial gas, even if a large amount of inflow is
allowed for during the first few x 10E+8 years. This is because some
pre-enrichment is required for lines in the bulk of the stars to approach the
observed line-strengths in ellipticals.Comment: 18 pages, 8 figures, Latex, accepted for publication in MNRA
On the relation between viscoelastic and magnetohydrodynamic flows and their instabilities
We demonstrate a close analogy between a viscoelastic medium and an
electrically conducting fluid containing a magnetic field. Specifically, the
dynamics of the Oldroyd-B fluid in the limit of large Deborah number
corresponds to that of a magnetohydrodynamic (MHD) fluid in the limit of large
magnetic Reynolds number. As a definite example of this analogy, we compare the
stability properties of differentially rotating viscoelastic and MHD flows. We
show that there is an instability of the Oldroyd-B fluid that is physically
distinct from both the inertial and elastic instabilities described previously
in the literature, but is directly equivalent to the magnetorotational
instability in MHD. It occurs even when the specific angular momentum increases
outwards, provided that the angular velocity decreases outwards; it derives
from the kinetic energy of the shear flow and does not depend on the curvature
of the streamlines. However, we argue that the elastic instability of
viscoelastic Couette flow has no direct equivalent in MHD.Comment: 21 pages, 3 figures, to be published in J. Fluid Mec
Auditing the TPACK confidence of Australian pre-service teachers: the TPACK confidence survey (TCS)
This chapter describes the construction and validation of an instrument to measure teachers’ Technological Pedagogical Content Knowledge (TPACK). The TPACK Confidence Survey (TCS) contains scales that measure teachers’ attitudes toward using ICT; confidence to use ICT for teaching and learning tasks (TPACK); competency with ICT; Technology Knowledge (TK); and TPACK Vocational Self-efficacy. The scale measuring TPACK confidence uses the Learning With ICTs: Measuring ICT Use in the Curriculum instrument that has been evaluated and reported previously. This paper proposes that the TCS provides a valid and reliable instrument with which to audit teachers’ TPACK confidence
The Early Promise of TBRI Implementation in Schools
The program known as Trust Based Relational Intervention® (TBRI®) began as an exploration into the detrimental behaviors of foster and adopted children placed in homes with unsuspecting caregivers who assumed their living environment would result in positive results rather than fear based emotions and behaviors. The researchers at the Karyn Purvis Institute of Child Development (KPICD) at Texas Christian University held summer camps for adopted children and through that work developed an intervention to meet the needs of children who had experienced trauma. KPICD identifies these young people as “children from hard places” (Purvis & Cross, 2005). Copeland et al (2007) reported that an estimated 68% of children in the United States have experienced some sort of trauma. This astounding statistic holds great meaning for teachers and administrators, because these children from hard places routinely manifest aggressive and undesired behaviors due to an altering of their physiology. The literature on TBRI® at this point mostly has chronicled success with families, group homes and summer camps (McKenzie, Purvis, & Cross, 2014; Howard, Parris, Neilson, Lusk, Bush, Purvis & Cross, 2014; Purvis & Cross, 2006). TBRI® has only recently been implemented in school settings. This report provides an overview of the impacts of trauma, trauma related work in schools, and the four articles published to this point related to the use of TBRI® in schools
A self-sustaining nonlinear dynamo process in Keplerian shear flows
A three-dimensional nonlinear dynamo process is identified in rotating plane
Couette flow in the Keplerian regime. It is analogous to the hydrodynamic
self-sustaining process in non-rotating shear flows and relies on the
magneto-rotational instability of a toroidal magnetic field. Steady nonlinear
solutions are computed numerically for a wide range of magnetic Reynolds
numbers but are restricted to low Reynolds numbers. This process may be
important to explain the sustenance of coherent fields and turbulent motions in
Keplerian accretion disks, where all its basic ingredients are present.Comment: 4 pages, 7 figures, accepted for publication in Physical Review
Letter
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